Got sent this through the post. Worth using for my blogging site? Or is it just to suck me into eventually paying out more in the longrun?
Obviously it's designed to get you to start using adwords, but that doesn't mean it won't be worth it. Then again, it doesn't mean that it will, either. It's all down to how you manage spend and target your ads, and whether the thing you are advertising is conducive to the type of traffic that adwords provides. It's worth identifying what goals you'd have for an adwords campaign (sales, subscribers, followers, repeat visitors etc.) upfront, so you can tailor your ads/keywords and more effectively measure the results of the campaign. Be aware that there are usually startup charges that vary by region, so even if you have the $50 voucher you'll need to pay ~$5 upfront to activate your account.
You have to use it fast, like within 2 weeks or something before your coupon / voucher expires. Your AdWords account has to be new too. You can insert your voucher number at the Billing tab.